Balancing device



.lune 29, 1937. w. E. .JOHNSON v 2,085,588

v BALANGING DEVICE Filed oct. 24; 1935 I' 'HAMA/cf E Inventor: l

is Attorrweg.

Patented June 29, 1937 UNITED STATES PATENT OFFICE BALANCING DEVICE of New York Application October 24, 1935, Serial No. 46,568

s claims.

My invention relates to balancing devices` and more particularly to balancing devices especially adapted for use in connection with refrigerant compressors, or the like.

Refrigerating machines ordinarily include a refrigerant compressor in Which vaporized refrigerant is compressed in one or more cylinders by suitable reciprocating pistons, the latter usually being driven by an electric motor. During the reciprocation of the compressor pistons in their respective cylinder bores, they are rapidly accelerated in one direction, then decelerated as they approach the end of their travel in that direction, then rapidly accelerated in the oppo site direction and again decelerated as they appreach the end of their travel in this opposite direction. By the term pistons I, of course, intend to include not only the pistons themselves, but the other parts attached thereto which also have a reciprocatory movement. This rapid acceleration and deceleration of the pistons in opposite Ydirections is opposed by the inertia of the pistons,`which tends to cause them to maintain a motion of constant velocity in any particular direction in which they may move. That is, an inertia force is set up b-y the pistons, which varies directly as the rate of change of velocity i of movement of the` pistons and, Which reacts on the driving shaft of the Idriving motor and, consequently, on other apparatus attached thereto.V This inertia force is thus of a reciprocatory or vibratory character and results in an undesirable vibration of the driving motor and com-A pressor. Such a vibration of the parts of the refrigerating machine Which,of course, increases the noise of its operation is particularly undesirable in tne case of machines, designed for household use, for cooling either a room or a food storage compartment of a refrigerator cabinet. Since a refrigerant compressor of the recipro-` cating type ordinarily operates at a substantially constant normal running speed, the frequency of the forces applied thereto, dueto the inertia of the reciprocating parts, is also substantially constant.Y It has been, heretofore, proposed in bal-l ancing masses, subjected to a vibratory force of constant frequency, to attach thereto a second mass by means of a spring or other resilient connection having such characteristics that the 'second mass has a natural frequency of vibration equal to the frequency of the disturbing force. In such case, the vibrations of the second mass are substantially 180 out of phase With respect to the disturbing force applied to the 5,5 first mass and the inertiaforce of` the second mass, Which is thus exactly opposite in time phase, cancels the applied force. The net result is that the first mass remains substantially stationary. Such an arrangement is ordinarily termed a dynamic balancer. It is obviously not feasible to use a dynamic balancer of this type on a compressor piston, for example, since the piston must have a reciprocatory motion in order to perform its primary compressing function in the machine. 10

It is an object of my invention to provide an improved balancing arrangement for the reciprocating parts of a refrigerant compressor, or the like, in Which the reciprocating parts of the compressor move with a substantially `constant l5 periodicity and amplitude of movement and in Which the inertia forces, resulting from such movement, are exactly balanced. I accomplish this by providing a balance Weight, or similar mass, which cooperates with the moving parts to be balanced through a suitable resilient connection. The lresilient connection is so arranged that the entire system, composed of the reciprocating parts of the compresso-r, the balance Weight, and the resilient connection, has a combined natural frequency `of vibration substantially equal to the frequency of the inertia forces set up by the reciprocating parts of the `compressor, as contrasted With the ordinary dynamic balancer in which the balance Weight and resil- 30 ient connection alone have a natural frequency of vibration equal to the frequency of the disturbing forces applied to the mass which is to be balanced. s

I have found, however, that difliculty is en- `35 countered in the operation of a balancing device of the general preferred type, described above, during the periods Ain Whichthe inertia forces to `be balanced are of a lower frequency than `the natural frequency of the system here- 40 tofo-re defined as, for example, during the starting period of the machine. Thus, during the starting period of the machine, the frequency of the inertia forces set up by the reciprocating parts of the machine gradually increases from a 45 value of zero, when the machine is at rest, to a normal maximum value at full running speed.

At some point between these tWo values of frequency, the inertia forces attain a frequency which is just equal to the natural frequency of 50` the balance Weight and its resilient connection alone. Consequently, a condition of resonance is had in which the balance weight tends to have an infinite amplitude of vibration which, in practice, is limited only by friction and the obstruction afforded to the movement of the balance weight by its: mounting. At a result, the balance weight vibrates with such great force at this resonance speed that a severe pounding in the machine ensues. If a coil spring, 'for example, is used as the resilient connection for the balance weight, it will be completely collapsed by the balance weight and a heavy blow is delivered to the machine when the spring thus collapses or goes solid. If this condition persisted only at a speed of the machine at which this resonant condition rst occurred and then stopped as soon as a higher speed was reached,-

it might be possible to accelerate the machine with sufficient rapidity that the resonant point could be passed without inflicting serious injury on the machine. I have found that this is not the case, however, but that on the other hand when such a pounding of the balance weight once starts during a period of resonance that it continues at all higher speeds, so that a proper operation of the balancing device is never had. This apparently results from the fact that the shock of the impact on the balance Weight when its lconnectingspring collapses imparts an added restoring force thereto tending to move the balance weight in the opposite direction at an even higher speed than the compressed spring itself would normally accomplish. Consequently, the effective natural frequency of the balance weight and its resilient connection is progressively increased in direct proportion to theincrease in speed of the machine and a condition of pseudoresonance results in which the pounding of the balance weight continues with steadily increasing force at all higher speeds.

It is a further object of my invention to provide a balancing device of the type described for a refrigerant compressor, or the like, in which the reciprocating parts of the machine, a balance Weight, and a resilient connection therebetween form a dynamic system having a combined natural frequency substantially equal to the frequency of the inertia forces set up by the moving parts of the compressor at the normal running speed of the compressor and an arrangement for preventing a pseudo-resonance condition in the machine, due to the action of the balanced weight, when the machine is operating at other than its normal running speed. I accomplish this by providing an arrangement for varying the rate of change in the force applied to the balance weight by the resilient connection therefor when the amplitude of movement of the balance weight reaches a predetermined maximum. By so varying the rate of change in the ing, in which Fig. l is a side elevation, partly in section, of a refrigerant compressor provided with a balancing device embodying my invention; Fig. 2 is an enlarged sectional bottom plan View along the line'2-2 in Fig. 1 of the balancing'device vand a portion of the compressor shown in Fig. 1;' and Fig.r 3 is a graph illustrating the relation of the amplitude of movement of the compressor reciprocating parts and of the balance weight therefor with respect to variations in speed of the compressor drive shaft, for the machine illustrated in Figs. l and 2.

Referring to the drawing, I have shown in Fig. 1 a refrigerant compressor il) of the Scotch yoke type designed for household use and which is driven by an electric driving motor II having a vertical driving shaft I2. The compressor I0 includes a cylinder I3 having a horizontal cylindrical bore I4. A horizontal cylindrical reciprocatable member or piston I5 is reciprocated in the cylinder bore If by the driving motor II. In the illustrative form of my invention, the driving motor II is connected to the compressor piston I5 through a Scotch yoke mechanism which includes a cylindrical cross yoke i6 which is rigidly secured to the outer end of the piston I5 at right angles thereto. A cylindrical slide block Il is slidably mounted in the yoke I5 and has a vertical cylindrical hole I8 formed therein which receives an eccentric crank pin i9. It will be noted that the crank pin I9 extends through an elongated slot i60. formed in the bottom of the yoke I5. A rotating counterweight 20 is rigidly secured to the top of the motor driving shaft i2 and the crank pin I9 is rigidly secured to the top of the counterweight 2E! eccentrically with respect to the motor driving shaft I2. Upon rotation of the motor driving shaft I2, the compressor piston I5 is reciprocated in the cylindrical bore I4, the slide block I'I having a reciprocating motion in the yoke I 6.

In the operation of the refrigerant compressor, described above, the rotating forces or couples which would otherwise tend to cause a vibration of the machine are balanced by a suitable set of rotating counterweights, one of which is indicated at 20. Due to the inertia of the reciprocating piston I5, reciprocatory forces are applied to the compressor tending to cause vibration of the same during its normal operation. Since the compressor I0 normally operates at a constant running speed, the frequency of the reciprocatory disturbing forces applied thereto is also substantially constant during such normal operation.

I have provided a balancing device embodying my invention for the refrigerant compressor IU in which a reciprocatable balance weight 2I is utilized to balance or counteract the reciprccatory or vibratory inertia forces exerted on the compressor by the piston mechanism. The balance Weight ZI is cylindrical and is provided with laterally extending cylindrical projections 22 and 23 on the opposite sides thereof. A cylindrical bore 24 extends axially through the counterweight 2I and the projections 22 and 23, the longitudinal axis of the bore 24 being substantially coincident with an axis of symmetry of the counterweight 2| and its projections 22 and 23. 'Ihe counterweight 2l is slidably mounted on the cylindrical guide rod 25 which is positioned in the bore 24 formed therein. The inner end of the guide rod 25 is rigidly secured to the side of the yoke I6 which forms a part of the piston mechanism and the guide rod 25 is arranged substantially in alignment with the piston I5. The cuter end of the guide rod 25 is slidably supported in a bore 2E formed in the upper end of an L-shaped bracket 2l, the lower end of which is secured to the top of the driving motor II by a bolt ZB.

The balance weight 2i is biased to a predetermined position with respect to the piston mechanism by a resilient arrangement exerting a variable biasing force thereon proportional to the amplitude of displacement of the balance weight which preferably includes a pair of helical compression springs'29 and 39 positioned on opposite sides `of the balance weight 2| and surrounding the guide rod-25. The inner ends of the springs 29 and 39 surround the lateralprojections 22 and `23 of the balance weight 2| and are tightly fitted in suitable helical grooves formed in the surfaces of the lateral projections -22 and 23. The inner ends `of the springs 29 and 39' are thus rigidly secured tothe balance weight 2|. VThe `axial or lateral i movement Vof the springs 29 and 39 'is limited bya pair of stops or collars 3| and 32 which are rigidly secured to the guide rod 25 by pins 33 and 34, respectively. v

" The collars 3| and 32 are positioned sufficiently close together on the guide rod 25 that both of the springs 29 and 39 are somewhat compressed even when the balance weight 2 Iris at rest. The mass of the balance weight 2| is so proportioned with respect to the masses of the reciprocating parts of 32 and with respect to the resilient characteristics of-the springs 29 and 39 that the entire dynamic system, `composed of reciprocating parts of the compressor, the balance weight 2| and the springs 29 and 39 will have a natural frequency of vibration substantially equal to the frequency of the reciprocatory forces resulting from the inertia of the reciprocating parts of the compressor. I have found that, if the outer ends of the springs 29 and 39 are fixed with respect to the guide rod 25, that difficulty is experienced in operating the mechanism, described above, especially during the acceleration period of theV compressor. During the starting period of the machine, the frequency of the inertia forcesset up by the reciprocating parts ofthe machine gradually increases from a value of zero; when 4the machine is at rest, to a normal maximum value at full running speed. At some point between these two values of frequency, the inertialforces attain a frequency which is just equal to the natural frequency of the balance weight 2| and its resilient connecting springs 29 and39. Consequently, if the outer ends of the `springs 29 `and 39 are fixed with respect to the guide rod 2-5, a condition of resonance is had in which the `balance weight 2| tends to have an infinite amplitude of vibration which is, in practice, limited only by friction and-by thelobstruction afforded to its movement by the collars 3| and 32. Asa result, the `balance weight Vibrates with such great force at this resonance speed that it p ounds heavily against thecollars 3| and 32. The'helical springs 29 and 39 are completely `collapsed by the balance weight 2| and a heavy blow is transmitted therethrough to the collars 3| and 3 2. I have found that when this pounding of the balance weight once starts during such a period of resonance that it continues at all higher speeds sothat a proper operation of the balancing device is not'attained.

In order to overcome this difficulty, I have provided 'a` pair of cylindrical springfplugs35 and 36V which are slidably mounted on the guide rod 25. The outer ends of the helical springs 29 and 39 are tightly fitted in suitable helical grooves formed in the surfaces ofthe spring plugs 35 and 36 andare thus` rigidly secured thereto. It will thus be seen that the outer ends of the springs 29 and 391are `freeto move `with respect to the Vguiderod25 `after the balance Weight 2| passes through a predetermined amplitude Vof reciprocation. Washers 31 and 38, made of i'lber, felt, or other sound-deadening material, are preferably positioned on the inner faces of the collars 3| and 32, in order to minimize any noise which might otherwise result from the striking of the spring plugs 35 and 36 against the collars 3| and 32, respectively.

Since the spring plugs 35 and 36 are movable with respect to the guide rod 25 when the balance weight 2| attains a predetermined amplitude of reciprocation, the spring constant or rate of change in the force applied to the balance weight 2| by the springs 29 and 39 is also changed when this predetermined amplitude of movement of the balance weight 2| is attained. By so decreasing the rate of change in the force applied to the balance weight 2|, its natural frequency of vibration on the springs 29 and 39 is varied and, consequently, the resonant or pseudo-resonant condition is avoided and it is possible to accelerate the compressor on up to its normal running speed without having the balance weight 2| pound the collars 3| and 32 due to such a pseudo-resonant condition.-

In the operation of the machine, described above, when the driving motor is started the driving shaft I2 is rotated at a gradually increasing speed and, similarly, the compressor piston I5 is reciprocated at a gradually increasing speed although with a constant amplitude of movement. When the piston |5 and guide rod 25 are first slowly reciprocated, the balance weight 2| moves back and forth substantially in phase therewith since there is sufficient friction between the balance weight 2| and the guide rod 25 to cause the balance weight to reciprocate with the rod. As the speed of the compressor piston I5 is increased, however, the balance weight 2|i gradually begins to reciprocate with a steadily increasing amplitude due to its inertia. The springs 29 and 39 exert a restoring force on the balance weight 2| tending to move it back to its predetermined position with respect to the guide rod 25 against the action of the forces set up by the inertia of the balance weight 2|.

ien the speed of the compressor reaches such a value that the frequency of the inertia forces set up by the reciprocating parts of they compressor is substantially equal tothe natural frequency of the balance weight 2i and springs 29 and 39, a resonant condition is had in which the balance weight tends to reciprocate substantially 180 outV of phasewith respect to the piston l5 and with an. infinite amplitude of movement. As soon as the balance weight moves far enough to the right, for example, that the spring 29 is no longer compressed the spring plug 35 moves to the right away from the collar 3|. At this instant the spring constant or, in other Words, therate o-f change in the forces applied to the other Weight 2| by the springs 29 and 39 is chan-ged. In. order for the rate of change in the force applied `by the springs 29 and 39 to be constant the outer end of the spring 29 would have to be xed so that the therefore decreasing compressive force exerted by the spring 29 on the'balance weight 2| would become negative, that isfsoy that the spring 29 would be in tension. Since in the arrangement which I have provided, however, Vthe rate of change in the force appliedtoi the balance weight 2| by the springs. 29 and 39 does: change, as soon as. the balance weight 2| reaches this predeter- CII springs Y29 and 30 is at once lowered and, consequently, the resonant condition no longer prevails since the natural frequency of the balance Weight and springs 29 and 30 does not coincide with the frequency of the inertia forces applied thereto by the reciprocating parts of the compressor.

As heretofore pointed out, the masses of the reciprocating parts of the compressor and the mass of the counterweight 2|, as Well as the resillent characteristics of the springs 29 and 30, are so proportioned that the dynamic system, composed of the reciprocating parts of the compressor, the balance Weight 2|, and the springs 29 and 30, has a natural frequency substantially equal tothe frequency of the inertia forces set up by the reciprocating parts of the compressor. Consequently, these inertia forces are exactly balanced by the out of phase inertia forces set up by the balance weight 2| in the dynamic system defined. This action is graphically illustrated in Fig. 3, which represents the amplitude of reciprocation of the piston as Well as of the balance weight 2| at various speeds of rotation of the drive shaft I2. The curves'shown in Fig. 3 are plotted for a construction in which the inertia of the reciprocating parts of the compressor is substantially equal to the inertia of the balance Weight 2|. In that case, the inertia forces set up by the reciprocating parts of the compressor will be exactly balanced by the balance Weight 2| when the amplitude of reciprocation of the reciprocating parts of the compressor is' exactly equal to the amplitude of reciprocation of the balance Weight 2| and opposite in phased relation thereto. From an inspection of Fig. 1 it will be seen that the piston mechanism, that is, the reciprocating' parts of the compressor has a constant amplitude of reciprocation as is, of course, necessary due to the construction of the machine. It will be seen that as the speed o-f the machine increases, the amplitude of the reciprocation of the balance Weight increases until it tends to become infinite at approximately 15 cycles per second which is substantially the resonant speed of the machine illustrated. At this point the reciprocation of the balance Weight 2| becomes 180 out of phase with respect to the inertia forces set up by the piston mechanism. From that point on, the amplitude of reciprocation of the balance Weight 2| gradually decreases until at the normal running speed of the machine which is about 30 cycles per second in the machine illustrated. The amplitude of reciprocation of the piston mechanism and balance weight 2| are both equal to the same value A.

From a consideration of the graphical illustration of the operating characteristics of my improved balancing device shown in Fig. 3, it Will be seen that the balancing device is effective in counteracting the inertia forces set up by the piston mechanism at all speedsabove the resonant speed of the balance Weight 2| on the springs 2S and 30. This fact is of particular importance inVv that it allows a fairly wide latitude of error in the design, as well as the manufacture ofthe various parts of the machine. This is true since a condition of approximate balance is had at all speeds close to the normal running speed and even at those varying an appreciable amount therefrom. 'I'his characteristic operation of my improved balancing device .is very different from that prevailing in an ordinary Kfdynamic balancer of the type heretofore described. That is, in an ordinary dynamic balancer, the balance Weight is effective in maintaining the body to be balanced in a substantially stationary condition only at the critical resonant speed indicated in the graph in Fig. 3. It Will be seen that the action of the balance Weight varies sharply with aV slight change in speed from the critical value and, consequently, a careful design of theparts as Well as great care in the manufacture thereof would be required.

While I have shown a particular embodiment of my invention in connection with a refrigerant compressor designed for' household use, I do not desire my invention to be limited to the particular construction shown and described and I intend, in the appended claims, to cover all modications within the spirit and scope of my invention.

What I claim as neW and desire to secure by Letters Patent of the United States, is:

1. In combination, a compressor or the like including a reciprocatable member exerting a vibratory force thereon of substantially constant frequency when said compressor is operating at its normal running speed, a balancing device therefor comprising a reciprocatable balance Weight, means for resiliently connecting said balance weight and said reciprocatable member and for mounting said balance Weight on said reciprocatable member and movably with respect thereto, the inertias of said reciprocatable member and said balance Weight being proportioned with respect to the elastic characteristics of said resilient means to form a dynamic system composed of said reciprocatable member and said balance Weight and resilient means having a combined natural frequency of reciprocatory oscillation substantially equal to said constant frequency of said vibratory force, and means for reducing the force applied to said balance weight by said resilient connection when the amplitude of reciprocation of said balance Weight reaches a predetermined maximum.

2. In combination, a compressor or the like including a reciprocatable member exerting a vibratory force thereon of substantially constant frequency when said compressor is operating at its normal running speed, a balancing device therefor comprising a reciprocatable balance Weight, means resiliently exerting a variable biasing force on said balance Weight proportional to the amplitude of reciprocation thereof for biasing said balance Weight to apre-determined position with respect to said reciprocatable member and for mounting said balance Weight on said reciprocatable member and movably with respect thereto, said reciprocatable member and said balance Weight and said resilient means having a combined natural frequency of reciprocatory oscillation substantially equal to said constant frequency of said vibratory force, and means for reducing the rate of variation of said biasing force exerted on said balance Weight by said resilient means during the acceleration period of said compressor when the amplitude of reciprocation of said balance Weight reaches a predetermined maximum to prevent a pseudoresonance condition in the system composed of said reciprocatable member and balance Weight and resilient means during such acceleration period. 3. In combination, a compressor or the like including a reciprocatable member exerting a vibratory force thereon of substantially constant frequency when said compressor is operating at its normal running speed, a balancing device therefor comprising a reciprocatable balance Weight, means including compression springs positioned on opposite sides of said balance weight and exerting a variable force on said balance Weight proportional to the amplitude of reciprocation thereof for biasing said balance Weight to a predetermined position with respect to said reciprocatable memberand for mounting said balance weight on said reciprocatable member and movably with respect thereto, said reciprocatable member and balance Weight and resilient means having a combined natural frequency of reciprocatory oscillation substantially equal to said constant frequency of said vibratory force, and means for reducing the rate of variation of `said biasing force exertedv on said balance A weight by said resilient means during the acceleration period of said c 'ompressor when the a pseudo-resonance condition in the system composed of said reciprocatable member and balance weight and resilient means during such acceleration period.

`4. In combination, a compressor or the like including a reciprocatable member exerting a vibratory force thereon of substantially constant frequency When said compressor is operating at its normal running speed, a balancing device therefor comprising a reciprocatable balance weight, means including a guide rigidly secured to said reciprocatable member for slidably supporting said balance Weight, resilient means including compression Springs positioned on opposite sides of said balance Weight and exerting a variable biasing force on said balance Weight proportional to the amplitude of reciprocation thereof for biasing said balance Weight to a predetermined position With respect to said reciprocatable member, said reciprocatable member and balance Weight and resilient means having a combined natural frequency of reciprocatory oscillation substantially equal to said constant frequency of said vibratory force, and means for reducing the rate of variation of said biasing force exerted on said balance weight by said resilient means during the acceleration period of said compressorrwhen the amplitude `of reciprocation ofsaid balance Weight reaches a predetermined maximum to prevent a pseudoresonance condition in the system composed of said reciprocatable member and balance Weight' period.

5. In combination, a compressor or the `like lincluding a reciprocatable piston exerting a vibratory force thereon of substantially constant frequency When said compressor is operating at its normal running speed, a balancing device therefor comprising a reciprocatable balance Weight, means including a guide rod rigidly secured to said piston in axia1 alignment therewith for slidably supporting said balance Weight, resilient means including compression springs rigidly secured to opposite sides of said balance Weight and surrounding said guide rod for biasing said balance Weight to a predetermined position with respect to said piston, said piston and balance Weight and resilient means having a combined natural frequency of reciprocatcry oscillation substantially equal to said constant frequency of said vibratory force, spring plugs slidably mounted on said guide rod and secured to the outer ends of said compression springs, and means including stops for limiting the axia1 movement of said spring plugs, said stops being positioned to slightly compress said springs when said compressor is at rest.

6. In combination, a compressor or the like including .a reciprocatable piston exerting a vbratory force thereon of substantially constant its normal running speed, a balancing device therefor comprising a balanceweight having laterally extending projections formed thereon and having a bore extending therethrough` and through said lateral projections, means including a guide rod positioned in said bore and rigidly secured to said piston in axial alignment there- With for slidably supporting said balance Weight, resilient means "including helical compression springs surrounding said guide rod and having their inner ends secured to said lateral projections on said balance Weight for biasing said' balance Weight to a predetermined position with respect to said piston, said piston and `balance Weight and resilient means having a` combined natural frequency of reciprocatory oscillation substantially equal to said constant frequency of said vibratory force, means for slidably supporting the outer ends of Said springs on said guide rod, means including stops positioned on said guide rod for limiting the axial movement of said compression springs and balance Weight, and means for minimizing the noise resulting lfrom the striking of said springs against said 

